The present invention relates to a method for recording a large amount of information on a magnetic recording medium at one time, and in particular, to a method for transferring a recording information to a magnetic recording medium of large capacity and high recording density.
With rapid development and progress in the utilization of digital image, amount of information to be handled in personal computers and other devices has extensively increased. Because of the increase of the amount of information, there are now strong demands on a magnetic recording medium, which has larger capacity to record the information and can be manufactured at low cost and requires shorter time for writing and reading operations.
In a high density recording medium such as hard disk or in a high density floppy disk type magnetic recording medium represented by ZIP (Iomega Inc.), information recording area has narrower track compared with the floppy disk now commonly used. In order that magnetic head can scan over narrow track width and signals can be recorded or reproduced with high S/N ratio, it is necessary to perform accurate scanning by the tracking servo technique.
In a large capacity magnetic recording medium such as a hard disk or a removable type magnetic recording medium, servo signal for tracking or address information signal, reproduction clock signal, etc. are recorded with a certain spacing between them within one turn of the disk. This is the so-called pre-format.
By reading this pre-formatted signal and by correcting its own position, the magnetic head can run accurately on the track.
In the mode of pre-formatting currently in practice, disks are recorded one by one and track by track using a special-purpose servo recorder. However, there are problems in that the servo recorder are expensive and long time is required for the preparation of the pre-format and this means longer time for manufacture and higher manufacturing cost.
In this respect, a method has been proposed to perform magnetic transfer without carrying out pre-format for each track. For example, a transfer technique is described in Japanese Patent Publications Laid-Open 63-183623, 10-40544, and 10-269566. However, none of these inventions provides a proposal suitable for practical applications. There has been no disclosure on concrete means or conditions such as the condition of magnetic field to be applied at the magnetic transfer in the method for magnetic transfer or the means for generating the magnetic field.
To solve the problems as described above, the following method has been proposed in Japanese Patent Publications Laid-Open 63-183623 and 10-40544: On the surface of the substrate, surface irregularities (i.e. recesses and projections; concave portions and convex portions) corresponding to information signals are formed. The surface of the master carrier for magnetic transfer where ferromagnetic thin film is formed at least on the projections is brought into contact with the surface of sheet-type or disk-type magnetic recording medium where ferromagnetic thin film or ferromagnetic powder coating layer is formed. Or, AC bias magnetic field or DC magnetic field is applied to excite ferromagnetic material which constitutes the surface of the projections. As a result, magnetized pattern to match the surface irregularities is recorded on the magnetic recording medium.
According to this method, the surface of the projected portions of the master carrier for magnetic transfer is brought closely together to the magnetic recording medium to be pre-formatted, i.e. the slave medium, and the ferromagnetic material which constitutes the projected portions is excited. As a result, the desired format is formed on the slave medium. By this method, recording can be carried out statically without changing relative positions of the master carrier for magnetic transfer and the slave medium, and accurate pre-format recording can be performed. Also, the time required for the recording is very short. Specifically, in the method for recording from the magnetic head as described above, the time of several minutes to several tens of minutes is normally required, while magnetic transfer can be completed within one second regardless of the recording capacity or recording density in this magnetic transfer method.
Now, description will be given on the transfer of pattern for pre-format in the master carrier for magnetic transfer referring to FIG. 1. FIG. 1 (A) is a schematical plan view to explain magnetic layer surface of the master carrier for magnetic transfer, and FIG. 1 (B) is a cross-sectional view to explain the process of transfer.
On a certain area of the track of the master carrier 1 for magnetic transfer, a pre-format region 2 and a data region 3 where patterns of servo signals and address signal for tracking to be transferred are formed. By bringing the master carrier 1 for magnetic transfer and the slave medium 4 closely together and by applying an external magnetic field 6 for transfer in track direction 5, the pre-format information can be transferred to the slave medium as a recording information 7. Thus, the slave medium can be manufactured with high efficiency.
However, it has been made clear that, when magnetic transfer is performed according to this method, the quality of information signal may be deteriorated, and that servo action may be inaccurate.
It is an object of the present invention to provide a method and an apparatus for stable magnetic transfer by bringing a master carrier for magnetic transfer and a slave medium closely together and by transferring a pre-format pattern through application of an external magnetic field in order to prevent inaccurate servo operation of the slave medium.
It is another object of the present invention to provide a method for magnetic transfer and an apparatus for magnetic transfer for performing a series of processes including initial DC magnetization of the slave medium and the transfer of the recording information.
The object of the present invention can be attained by a method for magnetic transfer for applying magnetic field for transfer by combining a master carrier for magnetic transfer closely together with a slave medium, said master carrier having a magnetic layer formed on a portion corresponding to an information signal on surface of a substrate, and said slave medium receiving magnetic transfer, said method comprises a step of performing initial DC magnetization prior to the magnetic transfer under the condition that said master carrier for magnetic transfer is closely combined together with said slave medium.
The present invention also provides a method for magnetic transfer for applying magnetic field for transfer by combining a master carrier for magnetic transfer closely together with a slave medium, said master carrier having a magnetic layer formed on a portion corresponding to an information signal on surface of a substrate, and said slave medium receiving magnetic transfer, said method comprising the steps of applying magnetic field in track direction on the surface of the slave medium under the condition that said master carrier for magnetic transfer is closely combined together with said slave medium, and after performing initial DC magnetization in track direction on the slave medium in advance, of applying a magnetic field for transfer in track direction on the surface of the slave medium, and of performing magnetic transfer.
The present invention also provides the method for magnetic transfer as described above, wherein said method comprises the steps of generating a magnetic field, on a part in track direction, with magnetic field intensity distribution having a portion with magnetic field intensity by more than 1.5 times higher than coercive force Hcm of the slave medium at least at one point on a position in track direction, and of applying magnetic field for performing initial DC magnetization in track direction on the slave medium by rotating a combination unit comprising the slave medium and the master carrier for magnetic transfer combined closely together or by rotating the magnetic field in track direction.
The present invention also provides a method for magnetic transfer for applying magnetic field for transfer by combining a master carrier for magnetic transfer closely together with a slave medium, said master carrier having a magnetic layer formed on a portion corresponding to an information signal on surface of a substrate, and said slave medium receiving magnetic transfer, said method comprising the steps of generating a magnetic field with magnetic field intensity distribution for initial DC magnetization by more than 1.5 times higher than coercive force Hcm of the slave medium on a portion in track direction, and after the magnetic field for initial DC magnetization has been applied, under the condition that the slave medium is closely combined together with the master carrier for magnetic transfer so that the magnetic field for magnetic transfer is applied on the surface of the slave medium, of applying magnetic field in track direction on the surface of the slave medium under the condition that the master carrier for magnetic transfer is closely combined together with the slave medium by rotating the combination unit or the magnetic field, and of performing magnetic transfer by applying the magnetic field for transfer to the surface of the slave medium immediately after the initial DC magnetization of the slave medium.
The present invention also provides the method for magnetic transfer as described above, wherein the coercive force Hcm of the magnetic layer of said master carrier for magnetic transfer is not more than 47.7 kA/m (600 Oe).
The present invention also provides the method for magnetic transfer as described above, wherein the coercive force Hcm of the slave medium receiving the magnetic transfer is not less than 143 kA/m (1800 Oe).
The present invention also provides the method for magnetic transfer as described above, wherein the direction of initial DC magnetization by applying magnetic field in track direction on the slave medium is in opposite direction to the magnetic field for transfer applied to perform magnetic transfer on the surface of the slave medium.
The present invention also provides the method for magnetic transfer as described above, wherein a portion with magnetic field intensity higher than the maximum value of the optimal transfer magnetic field intensity range is not present in any of track direction, and a portion with magnetic field intensity within the optimal transfer magnetic field intensity range is present at least at one point in one track direction, said method comprising the steps of generating a magnetic field with magnetic field intensity distribution where magnetic field intensity in track direction opposite thereto is lower than the minimum value of the optimal transfer magnetic field intensity range at a position in any track direction, and of applying magnetic field for transfer in track direction on the surface of the slave medium by rotating a combination unit of the master carrier for magnetic transfer closely combined together with the slave medium processed by initial DC magnetization in track direction or by rotating the magnetic field in track direction.
Further, the present invention provides a method for magnetic transfer according to claim 8, wherein the optimal transfer magnetic field intensity is in the range of 0.6xc3x97Hcm to 1.3xc3x97Hcm to the coercive force Hcm of the slave medium.
The present invention also provides an apparatus for magnetic transfer for applying magnetic field for transfer by combining a master carrier for magnetic transfer and a slave medium closely together, said master carrier having a magnetic layer formed on a portion corresponding to an information signal on surface of a substrate, and said slave medium receiving magnetic transfer, said apparatus comprising means for combining said master carrier for magnetic transfer with said slave medium closely together, initial DC magnetizing means for performing initial DC magnetization in track direction on the slave medium by applying magnetic field in advance in track direction on the surface of the slave medium under the condition that said master carrier for magnetic transfer is closely combined together with the slave medium, and transfer magnetic field applying means for applying magnetic field for transfer in track direction of the slave medium under the condition that said master carrier for magnetic transfer is closely combined together with the slave medium.
The present invention also provides an apparatus for magnetic transfer wherein the coercive force Hcm of the magnetic layer of said master carrier for magnetic transfer is not more than 47.7 kA/m (600 Oe).
The present invention also provides the apparatus for magnetic transfer as described above, wherein the coercive force Hcm of the slave medium receiving the magnetic transfer is not less than 143 kA/m (1800 Oe).
The present invention also provides the apparatus for magnetic transfer as described above, wherein the direction of initial DC magnetization by applying magnetic field in track direction on the slave medium is in opposite direction, on the surface of the slave medium, to the magnetic field for transfer applied for performing magnetic transfer.
The present invention also provides the apparatus for magnetic transfer as described above, wherein said initial DC magnetizing means has a portion with magnetic field intensity by more than 1.5 times higher than the coercive force Hcm of the slave medium only in one direction at a position in track direction, the magnetic field intensity is such that a magnetic field with magnetic field intensity distribution lower than the coercive force Hcm of the slave medium at any position in any track direction is generated at one portion in track direction, and a magnetic field for initial DC magnetization is applied in track direction on the slave medium by rotating the combination unit of the slave medium with the master carrier for magnetic transfer or by rotating the magnetic field in track direction.
The present invention also provides the apparatus for magnetic transfer as described above, wherein said transfer magnetic field applying means comprises means for generating a magnetic field in one portion in track direction, said magnetic field has such magnetic field intensity distribution that there is a magnetic field intensity higher than the maximum value in the optimal transfer magnetic field intensity range at any position in any track direction, that there is a magnetic field intensity within the optimal transfer magnetic field intensity range at least at one point in one track direction, and that a magnetic field intensity in track direction opposite thereto is lower than the minimum value of the optimal transfer magnetic field intensity range at any position in any track direction, whereby said apparatus comprises means for rotating a combination unit comprising the master carrier for magnetic transfer closely combined together with the slave medium processed by initial DC magnetization in track direction, or means for rotating the magnetic field in track direction to apply the magnetic field for transfer in track direction on the surface of the slave medium.
The present invention also provides the apparatus for magnetic transfer as described above, wherein said apparatus comprises means for applying initial DC magnetization by more than 1.5 times higher than the coercive force Hcm of the slave medium, means for applying magnetic field for magnetic transfer within the optimal transfer magnetic field intensity range in opposite direction to the magnetic field for initial DC magnetization, means for combining the slave medium with the master carrier for magnetic transfer closely together, and rotating means for rotating either the combination unit comprising the slave medium and the master carrier for magnetic transfer or the magnetic field in track direction, whereby magnetic field is applied in track direction on the surface of the slave medium under the condition that the slave medium is combined with the master carrier for magnetic transfer closely together, and immediately after the completion of initial DC magnetization in track direction of the slave medium, magnetic transfer is performed by applying the magnetic field for transfer in track direction of the slave medium under the condition that the slave medium is combined with the master carrier for magnetic transfer closely together.
The present invention also provides an apparatus for magnetic transfer as described above, wherein the optimal transfer magnetic field intensity is 0.6xc3x97Hcm to 1.3xc3x97Hcm.